Infectious bronchitis (IB) virus is a coronavirus that causes respiratory disease in domestic fowl (e.g., chickens). IB disease symptoms include, e.g., respiratory distress, reduced weight, reduced egg production, increased frequency of abnormal eggs, and increased rates of mortality.
Several different genotypes and serotypes of IB viruses have been identified. Genotyping of IB viruses is generally accomplished by sequencing all or part of the gene that encodes the S1 (spike) protein of the virus. The S1 protein is the N-terminal cleavage product of a larger S glycoprotein encoded by the genome of IB viruses. The C-terminal cleavage product of the S glycoprotein is referred to as the S2 protein. The S1 protein is responsible for cell attachment and is a major antigenic determinant for IB viruses. Exemplary genotypes (or “strains”) of IB virus include 793B, Massachusetts, Italy02, D274, Arkansas, B1648 and D1466. (See, e.g., Worthington et al. (June 2008), Avian Pathology 37:247-257).
A novel genotype of IB virus, designated “QX” (also referred to as “QXIBV”), was first identified in China in the late 1990s. (See Liu et al. (2006), Archives of Virology 151:1133-1148). Since the identification of the original QX genotype, numerous IB virus genotypes with a high degree of similarity/identity to QX at the S1 nucleotide sequence level have been identified worldwide. These “IB-QX-like” viruses (as further defined herein) have been identified, e.g., in France, Germany, Netherlands, Belgium, United Kingdom, Italy and Poland.
Clearly, IB-QX-like viruses pose a serious threat to the poultry industry. Notwithstanding the rapidly emerging significance of this type of IB virus, heretofore, no vaccines specific for IB-QX-like viruses have been available or described in the art. Commercially available IB vaccines (live, attenuated strains) have been found to be ineffective in protecting chickens against IB-QX-like viruses. Thus, there exists a need in the art for new vaccine compositions and methods of vaccination that provide specific protection against IB-QX and IB-QX-like viruses.